DESCRIPTION: Antibiotic resistance among common bacterial pathogens is a serious public health problem as it compromises our ability to treat infectious disease. The resistance problem is compounded by the relative lack of discovery of new antibiotics, especially those with novel mechanisms of action. Over the past several years Promiliad Biopharma has been developing new inhibitors that target the enzyme dihydrofolate reductase as a method of treatment for pathogenic bacteria, fungi and protozoa. Through our efforts and those of our collaborators, largely funded by STTR grants, we have discovered a class of antifolates characterized by a 2, 4- diaminopyrimidine and a biaryl domain linked through a three-atom propargyl bridge. This class of molecules is an important lead in the discovery of a new treatment for infectious disease. The current class of compounds, while potent antibacterial agents with activity against antibiotic resistant pathogens, currently lack sufficient metabolic stability. These compounds have short in vivo (and in vitro) half-lives which make progression to lead compound status somewhat difficult. We have found that by substituting a key fragment of the structure with a non-metabolizable bioisostere we can retain potency against a range of Gram positive pathogens while greatly improving selectivity and metabolic half-life. The goal of this project is o design, synthesize and assay additional bioisosteric analogs which display similar or better improvements in potency, metabolism and physical properties. Our goal in this Phase I application is to obtain a clear lead candidate. A Phase II project continuing from this work would then conduct IND-enabling experiments with the clear goal of filing an IND application.